package d1203.r2118.num06;

import javax.swing.*;

public class Demo01Integer {
    public static void main(String[] args) {
        Integer x = 20;
        int y = 30;
        String str = JOptionPane.showInputDialog("请输入圆的半径：");
        Integer r = Integer.valueOf(str);
        System.out.println(Math.PI * r * r);
    }
}
